Your loudspeakers are -6db at 28 hz. I can't guess the 3db point but a good sub will be flat into the low 20s. There still is some information down there that is worth exploring.
What does a subwoofer solve?
My previous amps were BHK 300 mono blocks. The bass they provided for my Monitor Audio PL 300ii speakers was exceptional. For several reasons I replaced the BHKs with a Luxman M900u. Very happy with the new amp, except for disappointing bass performance. Would a set of good subwoofers help resolve this, or do subwoofers only address a lack of bass in standard speakers?
Thanks in advance for any advice or suggestions.